Processions of the Rock and the space shuttle through the streets of L.A. recall the victory parades of ancient Rome. They redefine the city's civic identity.

The space shuttle Endeavour arrives at the United hangar at Los Angeles… (Anne Cusack, Los Angeles…)

It's not often that we get to compare Los Angeles to the Roman Empire, unless we're making fun of the kitschy copy-cat architecture of the Getty Villa. At least in popular stereotype, L.A. and Rome are polar opposites, each one the perfect foil for the other.

One city — ours — is unfinished, amnesiac and forward-looking; the other city — theirs — is so obsessed with past glory, its streets piled so high with landmarks and layers of history, that its 21st century personality can be tough to make out.

So when I began noticing similarities between an ancient Roman ritual and two huge public eventsin Los Angeles in 2012, I was tempted to dismiss them out of hand. Yet the more I dug into the comparison, the more it seemed to make sense: In parading both Michael Heizer's huge artwork "Levitated Mass" — better known as the Rock — and the space shuttle Endeavour along our boulevards within a single calendar year, Los Angeles is in some striking ways reenacting one of the oldest public celebrations in Western urban history, the Roman triumph.

In doing so, L.A. is marking a milestone in the way it frames its own history and defines its civic personality. The procession that brought the Rock to the Los Angeles County Museum of Art in March and the one that will carry Endeavour from LAX to the California Science Center starting Friday suggest that a certain exploratory phase in the life of the region has come to a close.

To put it bluntly: We used to make stuff here and send it out into the world or into outer space. Now we capture that stuff, tether it to the back of a huge vehicle and arrange a low-speed, celebratory public parade through the streets of Los Angeles before putting it on display in one of our major museums.

The triumph, in case you've forgotten your college classics lectures or haven't caught up with the HBO series "Rome" or the 1951 Deborah Kerr movie "Quo Vadis," was an elaborate procession held to commemorate a military victory — and by extension to promote the idea and the ideals of the Rome and its various territorial conquests.

In the most typical version, a victorious general would ride atop a chariot preceded by the spoils and enemy soldiers he'd captured. Often, this section of the triumph would include not just gold and jewels but also paintings of pivotal battles and, in some cases, architectural models of forts captured and towns seized.

Trailing behind, in a boisterous final group, were the troops, either chanting the ritual phrase "Io triumphe" — which essentially means "hooray, triumph" and also happens to be the name of the official Occidental College cheer — or singing rude songs about their leader.

The route generally began in Campus Martius, outside the traditional boundaries of the city, and proceeded past crowds of spectators in the Circus Maximus and through the Roman Forum before climbing to reach the Temple of Jupiter atop the Capitoline Hill.

Over time, the triumphs began to remake the architecture of the city. Rome shaped the triumphs, in other words, and then the triumphs shaped Rome.

The direct and indirect architectural products of the parades included not just triumphal arches but temples and other large public buildings financed with the spoils of war. These included the Temple of Minerva, a lavish restoration of the Temple of Hercules and — perhaps most dramatic of all — a theater dedicated to the general Pompey the Great, which the British historian Mary Beard, in her terrific 2007 book "The Roman Triumph," describes as a "combination of temple, pleasure park, theater and museum" that "wrote Pompey's name permanently into the Roman cityscape."

In a literal sense, of course, there are some obvious differences between the Roman triumph and the Rock and Endeavour parades. Heizer's sculpture wasn't accompanied by slaves, soldiers and piles of gold, and the shuttle won't be either.

Roman triumphs covered only about 21/2 miles through the compact ancient city; the Rock traveled more than 100 miles in total from a quarry in Riverside to LACMA, and Endeavour will be hauled 12 miles from LAX to the Science Center. And certainly our spin on the Roman ritual is a good deal less raucous and more secular.

But the symbolism of our parades is more than a little imperial. It suggests that the world and even the universe make up the empire from which we pluck our most prized possessions. And that in putting those possessions on public display we affirm some basic idea of what contemporary Los Angeles means or stands for.